# Quantum Data:Theoretical Requirements

1. Aug 23, 2008

### CJames

I'm curious as to the required number of qubits necessary for quantum data storage.

For example, suppose we had the technology to teleport the quantum state vector of a human body into quantum storage. Would the storage device require as many qubits as there are particles in the human body, or exponentially more?

Second, what would be required to simulate such a system in motion? I assume it would require the same number of qubits, but this is where you would need to introduce quantum logic gates. How many quantum logic gates would be necessary? What qualifies as a quantum logic gate to begin with?

I'm asking in the case of a human being simply because I'm writing sci fi, but the question holds the same for more likely scenarios such as simulating how proteins fold and so on.

2. Aug 24, 2008

### CJames

I can see that the answer likely relates to the Schrödinger equation. Unfortunately I don't really understand the Schrödinger equation at all...the number of required qubits must have something to do with the vector for the wavefunction, and the required number of quantum logic gates is probably related to the Hamiltonian operator. But I don't really understand where these things come from.

Regarding the Schrödinger equation...does the value for t have any effect on the complexity of the computation? That is, would it be just as easy for a quantum computer to output the state of the wavefunction as it would be in 1 second as in millions of years?

3. Aug 24, 2008

### f95toli

If you want to store one bit of information you need one qubit; I am not aware of any method that can be used to "package" information into qubits. The "quantumness" comes into play when we want to manipulate information, not store it.

A quantum logic gate is not that different from a conventional digital gate (AND, OR, XOR etc), the basic gate being a CNOT (controlled-not). However, not that the word "gate" is usually just used to denote an operation of some sort, i.e. a CNOT gate is usually realized using a sequence of electromagnetic pulses that interacts with (and therefore "operates on") a pair of qubits; meaning the gate is not really a piece of hardware.

I would suggest you get a copy of Krauss book "The Physics of Star Trek", in there you will find a discussion about how many bits are required to store a human (in the context of teleportation). However, the question is probably impossible to answer since we do not know how precise one would need to be, especially when it comes to our brain; would it be enough to record the position/state of of every cell or would you need to record the state of every atom? We don't really understand how the brain works so at the moment there is no way to answer that question.

4. Aug 24, 2008

### CJames

I've actually read the physics of star trek. Good book.

Thanks for the help, especially the clarification on the meaning of a quantum gate. But let me see if I can be more clear about what I'm talking about. What I'm envisioning here is a quantum computer that takes in the wavefunction of a quantum system, and outputs the wavefunction as it evolves with time. My understanding is that classical computers are unable to easily do so for wavefunctions with many variables, but quantum computers supposedly can.

What I'm most interested in knowing relates to the time it would take for these types of calculations to take place. For example, is it possible for a quantum computer to predict how a protein will fold in less time than it would take an actual protein to fold? And if a quantum system is chaotic, does it take more time for a quantum computer to predict the state of the wavefunction for a larger t?